This proposal is focused on the genetic and molecular examination of the Drosophila zw10 gene. Mutants in the zw10 gene disrupt chromosome segregation in both mitotic and male meiotic cells. Much of the interest in the ZW10 protein stems from its dynamic localization during mitosis. The PI and his collaborators argue that this protein may play a critical role in mediating kinetochore function and in signaling, or responding to, the presence or absence of tension on the kinetochore. The zw10 gene encodes an 85 kd protein with no significant homologies to other proteins of known function. The PI proposes a clever set of experiments designed to elucidate the function of this protein. Specifically, he proposes to (1) use immuno-EM and RT videomicroscopy to follow the temporal and spatial distribute of ZW10 at very high resolution; (2) investigate the consequences of injecting anti-ZW10 antibodies at various times; (3) assay the effects on ZW10 distribution of altering tension on chromosomes by Iaser surgery and by micro-manipulation; (4) determine whether modifications of the ZW10 protein (e.g. phosphorylation) are associated with its movements during the cell cycle; (5) perform a structure/function dissection of ZW10; (6) study the function of the ZW10 protein in C elegans.; (7) investigate the relationship of ZW10 to the products of other known genes; (8) identify proteins that interact with ZW10 by now standard biochemical and genetic means; and (9) begin the molecular analysis of a new gene, san, whose protein product appears to play an essential role in sister chromatid cohesion.